Does XJ750 have fuel overflows?

I can only spot the fuel hose from the tank and that's it?

The XJ manual wasn't very helpful and I'm not sure if mine are missing or there just aren't any.

( 84 XJ750RL)

 

Iirc the 1100's and 700's are the only bikes in the series with overflow (octopus) carb hoses. If the petcock is stock it should have one large nipple and one small nipple. The lg nipple feed the fuel rail. There should be a vacuum hose to the sm nipple from one of the intake boots (usually #3). The other three should be capped/clamped. Please post a pic so we can see the set up.

Gary H.

 

vid shows overflow for xj 700 if you have overflow tubes they come off the carbs and hang down

 

To my knowledge, the overflows were only fitted to bikes that were sent to North America.

 

Here are some pics. Looks like that one hose that rocs82650 was referring to is from carb 1 and is capped off due to now having a different petcock. On the right side of carb 4 there appears to be piping for a hose to go to but there's nothing there. No signs of fluid either so is it a universal piece that has no part in these carbs?

Cheers.

 

I'm pretty sure that those aren't the correct carbs for an XJ750 (per the book, but the book has been wrong before). It had Hitachi HSC33 carbs from the factory. Those are Mikuni carbs.

You've got a rare bike there. One of 887 built.

The ink stamps that denote what carbs you have might (maybe) still be visible. Look on the bottoms of the float bowls (the stamps can be anywhere on the carb, but the float bowls are the most comon location).

 

K-moe for the win!

Trying to run (unknown Mikuni's) in place of the stock Hitachi HSC33's could/will lead to all sorts of tuning (and other) issues........

 

+1 what k-moe and chacal said. PO swapped carbs and added pods. It's possible the exhaust isn't stock either. Jetting is going to be a nightmare.

Gary H.

 

But not impossible. My biggest concern is what the throat diameter of the carbs are, and if the slide springs were changed. If it were mine I'd see what the fuleing looks like without making any changes. Maybe he gets lucky and the PO got things dialed in.

 

When I first got the bike, it was a lot rougher than expected - (online purchase). I took it to a shop as whilst I'm handy, I was clueless. The shop did their thing and cleaned out the carbies.

The bike didn't have any filters on it when it arrived. I put on the K&N twin pods. The bike came with the exhaust as pictured below. The bike was near impossible to start and had really poor low end responsiveness.. With moving off, I'd have to rev the bike higher during friction point. I took it back and explained the starting and low end issues.

Admittedly all I wanted was a working bike and am not sure of what he did but now the bike starts with small use of the choke and the bottom end is much much better. I recall him saying that he had to widen something so it got more fuel, but what that was, I do not know and I at the time just wanted a working bike as I was still getting cold sweats about the purchase.

I think the almost straight through pipe is disturbing the low end responsiveness, but the bike was finally usable. The bike had great smooth power and I was quite surprised by the power it actually had.

I've since, had the electrical issues that I'm sorting through at the moment. Once I sort out the electrical prob and get a fuel tank mounted, I'll be able to ride the bike and get a proper feel for it all.

Once the bike shop opens up after the holiday period, I'll also pop back in and see what he actually did re the carbs.

My mindset has changed from 'I've bought a bike, lets go ride!' to, 'I've got one kick ass project that every now and again, I get to ride... until I have to repair the next weakest/oldest link'. The bike and I will both get there and from now on, I will do the repairs.

 

Take your time...it'll come together.

Gary H.

 

+1

The stock exhaust system is not very restrictive, so the pods are the larger culprit in your fueling issue. I'd call the shop and see if htey kept records of what was done to the fueling. Widening something has me thinking that jets were drilled out, or the needles shimmed. You need to know so that you aren't stabbing in the dark (particularly if the jets were drilled).

 

Called the mechanic today. He said they drilled the 'starter jets' which relate to the fuel going in during startup. Are there separate 'starter' and say 'general/running' jets?
Further I don't see how a startup alteration could further help the running low end responsiveness. Without having enough knowledge myself, is it correct in thinking they've drilled the jets (one jet per carb) and this has helped the startup and running of the bike?

Anything to be concerned about?

 

It is fairly possible they drilled the enrichment circuit jets because they were badly clogged up. If they did that with a bigger drill than needed, you're up for starting and idling problems.

 

I'm thinking that they drilled the pilots (pilot jets are often refered to as starter jets; see example below), and that makes it too rich when the enrichment circuit is fully in play.

I can't imagine any shop trying to drill out the enrichment jets since they are pressed into the float bowls. Heck, I can't hardly imagine a shop that even knows where the Hitachi enrichment jets are located unless they specialize in classic motorcycles.

example (note, this is not a Hitachi carb):

 

.... But if the DID drill the bowls, don' plan to use them on any other bike.... It would likely flood on trying to start it, unless you know just how to finess it...

 

Evening guys, I'm pulling the carbs apart now (with lots of pics).
Couple of questions at this stage;

1. Any chance anyone can guess the model of Mikuni carb?
2. How do I remove the bits circled red and orange and does the pin that holds the float punch out?

Cheers! (Literally, I'm 3 beers down in the garage with petrol fumes.. its definitely Saturday night)

 

Also would this type.of wear on a diaphragm warrant replacement?

 

Red:
-remove carb hat
-remove spring
- remove slide assembly
-now carefully drive the emulsion tube out from the red circle,through the slide bore

Float pivot
- it is slightly mushroomed so you will need to use a fine nail punch. MAKE SURE TO SUPPORT THE POST WITH THE FLOAT PIVOT HEAD AGAINST IT, or you will break it.

Yellow

Do NOT try to remove that. It is your enriched circuit pickup tube. That circuit does need to be cleaned though... that's a challenging one sometines.... but the tube is not removable

Diaphragm

Is it worn through? Replace it

Is it not worn through? Use it, but you can put a light thin and smooth dab of RTV to seal it

 

Hold the diaphram up to the light. If you see light through it, then repair it as Hogfiddles suggesed. I prefer to use liquid electrical tape as I find it easier to work with.